This invention relates to resid hydrotreating and, more particularly, to a process for increasing the conversion of 1,000+.degree. F. resid in a resid hydrotreating unit.
In the past, spiraling oil costs, extensive price fluctuations, and artificial output limitations by the cartel of oil producing countries (OPEC) have created instability and uncertainty for net oil consuming countries, such as the United States, to attain adequate supplies of high-quality, low-sulfur, petroleum crude oil (sweet crude) from Saudi Arabia, Nigeria, Norway, and other countries at reasonable prices for conversion into gasoline, fuel oil, and petrochemical feedstocks. In an effort to stabilize the supply and availability of crude oil at reasonable prices, Amoco Oil Company has developed, constructed, and commercialized extensive, multimillion dollar refinery projects under the Second Crude Replacement Program (CRP II) to process poorer quality, high-sulfur, petroleum crude oil (sour crude) and demetalate, desulfurize, and hydrocrack resid to produce high-value products, such as gasoline, distillates, catalytic cracker feed, metallurgical coke, and petrochemical feedstocks. The Crude Replacement Program is of great benefit to the oil-consuming nations by providing for the availability of adequate supplies of gasoline and other petroleum products at reasonable prices while protecting the downstream operations of refining companies.
During resid hydrotreating, such as under Amoco Company's Crude Replacement Program, resid oil (resid) is upgraded with hydrogen and a hydrotreating catalyst in a three-phase equilibrium of oil, catalyst, and gas bubbles to produce more valuable lower-boiling liquid products. In order to increase the efficiency, effectiveness, and profitability of resid hydrotreating, it is desirable to maximize the conversion of resid to more valuable lower-boiling liquid products.
The extent of conversion of resid to more valuable lower-boiling liquid products depends in part on the residence time of the resid in the reactor. During resid hydrotreating, hydrogen gas bubbles occupy a substantial portion of the reactor and thereby decrease the available space and residence time of the resid oil. Gas holdup can be reduced by decreasing the feed gas rate which then increases the liquid residence time. Decreasing the feed gas rate in such a manner, however, usually causes decrease of hydrogen partial pressure and subsequent coking of catalyst in the downstream reactors and loss of catalyst activity. Increasing the temperature of the reactor can increase the extent of conversion but can also increase catalyst coking and may be limited by the materials of construction of the reactor. Decreasing the resid feed rate into the reactor normally decreases the number of barrels of more valuable lower-boiling liquid products. Increased catalyst coking (coke formation) can lead to shutdown, extended downtime, increased frequency of repair, decreased efficiency, and reduced product quality.
It is, therefore, desirable to provide an improved hydrotreating process for increasing the conversion of resid which overcomes most, if not all, of the above problems. lems.